Hot Water Runs Out

spd1980

JakeCK said:

To elaborate on the hx and the principles it operates on:

The total interior surface area of the waste pipe is roughly 1200 sq in if I did my math right. Or about 8.4 sq ft. But that isn't the whole story. As the waste water drains it sticks to the ID creating a thin water film as it falls. If we really want to dig in we could start talking about the shape of water molecules and the slight differences in charge and all that chemistry and physics but that is beyond this conversation. Bottom line the waste water sticks to the ID as it falls straight down and, if plumbed right using counter flow, the fresh cold water enters the bottom of the hx to maximize delta T. The faster the fresh water flows the more you recover. This is why you want to have it piped to both go to the tank and the cold side of the shower faucet. And if you are using a tempering valve or thermostatic valve piped to both sides of that as well.

Thanks this will be helpful to assess whether the installer has experience with this type of solution.

spd1980

EBEBRATT-Ed said:

@spd1980 I don't agree with the above posts. I don't see how you could run out in 8 min. There are several things to check. 1. The 1" pipe to the indirect is slightly undersized 1 1/4" would be better. HTP want's the coil to have 10gpm from the boiler. But the run is short so I don't think that's the main issue. 2. HTP wants a flow of 10 gpm and the coils resistance is 7.9 feet of head. The taco 0015 @ 10 gpm will produce 9' of head. So what is left for the resistance of the pipe, fittings and valves is 1.1 feet of head (9-7.9) I calculated your pipe and fittings to about 5' of head. so your total head coil, pipe and fittings is at least 12.9' call it 13. and I didn't count the boiler and other fittings. At 13' of head the taco pump will do about 5.5 gpm not the 10 gpm you need. What I would do is put a digital thermometer on the supply and return pipes at the indirect to measure the boiler supply and return. You want a 20 degree TD (less is better) between the supply and return with the boiler running and drawing hot water out of the indirect. You could also up the boiler temp to 190 high limit but you shouldn't need to. Also the shower heads check the GPM you are drawing. Use a bucket. Catch the water for 30 seconds x2 that and you will have your gpm.

@EBEBRATT-Ed

Which circulator would provide enough gpm? Or would the pipe diameter need to be increased?

spd1980

JakeCK said:

To elaborate on the hx and the principles it operates on:

The total interior surface area of the waste pipe is roughly 1200 sq in if I did my math right. Or about 8.4 sq ft. But that isn't the whole story. As the waste water drains it sticks to the ID creating a thin water film as it falls. If we really want to dig in we could start talking about the shape of water molecules and the slight differences in charge and all that chemistry and physics but that is beyond this conversation. Bottom line the waste water sticks to the ID as it falls straight down and, if plumbed right using counter flow, the fresh cold water enters the bottom of the hx to maximize delta T. The faster the fresh water flows the more you recover. This is why you want to have it piped to both go to the tank and the cold side of the shower faucet. And if you are using a tempering valve or thermostatic valve piped to both sides of that as well.

@JakeCK

What are the pros and cons of a tempering valve vs a thermostatic valve? Which type is preferred? Can the output temperature of either be adjusted in case we want to mix down to 125 instead for example?

JakeCK

Mainly just accuracy as far as I know. 

mattmia2

Oh, the other things to think about, where the well is located in this tank, a good deal of the hot water has been consumed before the aquastat see that, so maybe 5-10 gal of your 35 gall are gone before it even makes a call to the boiler. If the boiler is set up as cold start and there hasn't been a recent heating call, you will be firing the boiler a while just to get it above the tank temp. Even worse the tank could be heating the boiler at the beginning.

You might try setting the boiler to warm start for a week or 2 and see if that makes a difference. Probably don't want to keep it that way because it will use a lot more fuel. Maybe there is a control that can do warm start only on a schedule or with a remote button.

george_42

simple solution , you and your wife shower together in one shower

EBEBRATT-Ed

@spd1980

To me you need a pump that will do 10 gpm @ about 15' of head. I have not selected a pump. Maybe Someone at Taco will respond like @Steve Thompson (Taco).

1. The 1" pipe to the indirect is slightly undersized 1 1/4" would be better. HTP want's the coil to have 10gpm from the boiler. But the run is short so I don't think that's the main issue.

2. HTP wants a flow of 10 gpm and the coils resistance is 7.9 feet of head. The taco 0015 @ 10 gpm will produce 9' of head.

So what is left for the resistance of the pipe, fittings and valves is 1.1 feet of head (9-7.9)

I calculated your pipe and fittings to about 5' of head. so your total head coil, pipe and fittings is at least 12.9' call it 13. and I didn't count the boiler and other fittings.

At 13' of head the taco pump will do about 5.5 gpm not the 10 gpm you need.

What I would do is put a digital thermometer on the supply and return pipes at the indirect to measure the boiler supply and return.

You want a 20 degree TD (less is better) between the supply and return with the boiler running and drawing hot water out of the indirect.

spd1980

Just wanted to say thanks again to everyone for all the help. 

The installer came today and set the high limit to 190 and they recommended a mixing valve which they will come back to install soon. If after that it’s still not resolved then I’ll do the shower heads next followed by the drain recovery system.

I know there’s only so many solutions but I’m glad the installer recommended the same solutions as everyone here advised so that gives me confidence in their abilities.

Regarding the high limit, I did notice the analog thermometer on the front of the boiler reads about 10 to 15 degrees less than the hydrostat reads. I wonder if I should bump the high limit up until the analog gauge reads 180. Unless the hydrostat has a way to adjust the temperature sensor offset to correct the temperature that it reads, but I didn’t see anything about that in the installation manual. 

EBEBRATT-Ed

I would take a temperature of the outlet pipe and compare it to the other temp readings. Then adjust the hydrostat as necessary to get the boiler outlet water to 190.

It's not unusual for the temp readings to not agree by 10 degrees or so depending on the flow through the boiler

spd1980

EBEBRATT-Ed said:

I would take a temperature of the outlet pipe and compare it to the other temp readings. Then adjust the hydrostat as necessary to get the boiler outlet water to 190. It's not unusual for the temp readings to not agree by 10 degrees or so depending on the flow through the boiler

@EBEBRATT-Ed

By outlet pipe do you mean right where the supply pipe exits the boiler?

What type of thermometer do you normally use to measure pipe temperature?